Rauisuchia
Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters) Triassic archosaurs. Originally it was believed that they were related to erythrosuchids,Sill, W. D. (1974). "The anatomy of Saurosuchus galilei and the relationships of the rauisuchid thecodonts". Bulletin of the Museum of Comparative Zoology 146: 317–362. ISSN 0027-4100. but it is now known that they are crurotarsans.Benton, M. J. (2004). Vertebrate Paleontology (3rd ed. ed.). Oxford: Blackwell Science Ltd. ISBN 0632056371. Three families are generally recognised: Prestosuchidae, Rauisuchidae, and Poposauridae, as well as a number of forms (e.g. those from the Olenekian of Russia) that are too primitive and/or poorly known to fit in any of these groups. There has been considerable suggestion that the group as currently defined is paraphyletic, representing a number of related lineages independently evolving and filling the same ecological niche of medium to top terrestrial predator. For example, ParrishParrish, J. M. (1993). "Phylogeny of the Crocodylotarsi, with reference to archosaurian and crurotarsan monophyly". Journal of Vertebrate Paleontology 13: 287–308. and JuulJuul, L. (1994). "The phylogeny of basal archosaurs". Palaeontologia Africana 31: 1–38. found poposaurid rauisuchians to be more closely related to Crocodilia than to prestosuchids. In a more recent study, NesbittNesbitt, S. J. (2003). "Arizonasaurus and its implications for archosaur divergence". Proceedings of the Royal Society B 270 (Suppl. 2): S234–S237. doi:10.1098/rsbl.2003.0066. ISSN 0962-8452. http://www.journals.royalsoc.ac.uk/content/2vetg3w8xha9e992. presented a different phylogeny with a monophyletic Rauisuchia. The group may even be something of a "wastebasket taxon". Determining exact phylogenetic relationships is difficult because of the scrappy nature of a lot of the material. However, recent discoveries and studies such as those of Batrachotomus''Gower, D. J. (2002). "Braincase evolution in suchian archosaurs (Reptilia: Diapsida): evidence from the rauisuchian Batrachotomus kupferzellensis". ''Zool. J. Linn. Soc 136 (1): 49–76. doi:10.1046/j.1096-3642.2002.00025.x. and restudies of other forms such as Erpetosuchus''Benton, M. J.; Walker, A. D. (2002). "Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland". ''Zool. J. Linn. Soc 136 (1): 25–47. doi:10.1046/j.1096-3642.2002.00024.x. ISSN 0024-4082. are shedding light on the evolutionary relationships of this poorly known but fascinating group. Both José BonaparteBonaparte, J. F. (1984). "Locomotion in rauisuchid thecodonts". Journal of Vertebrate Paleontology 3''' (4): 210–218. and Michael BentonBenton, M. J. (1984). "Rauisuchians and the success of dinosaurs". Nature '''310: 101. doi:10.1038/310101a0. argue that rauisuchians such as Saurosuchus developed an erect stance independently of and differently to dinosaurs, by means of having the femur vertical and angling the acetabulum ventrally, rather than having an angled neck or curve in the femur. They refer to this as the pillar-erect posture. The erect gait indicates that these animals were clearly active, agile predators, with locomotor superiority over the kannemeyerid dicynodonts and abundant rhynchosaurs on which they fed. They were successful animals, the largest with skulls up to a meter or more in length, and continued right until the end of the Triassic, when, along with many other large archosaurs, they were killed off by the end Triassic extinction event. With their demise, theropod dinosaurs were able to emerge as the sole large terrestrial predators. Meat-eating dinosaur footprints suddenly increase in size at the start of the Jurassic, when rauisuchians are absent.Olsen, P. E.; Kent, D. V.; Sues, H.-D.; Koeberl, C.; Huber, H.; Montanari, E. C.; Rainforth, A.; Fowell, S. J.; Szajna, M. J.; and Hartline, B. W. (2002). "Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary". Science 296: 1305–1307. doi:10.1126/science.1065522. PMID 12016313. Fossil record Well-known Rauisuchians include Ticinosuchus of the Middle Triassic of Europe (Switzerland and Northern Italy), Saurosuchus of the Late Triassic (Late Carnian) of South America (Argentina), and Postosuchus of the Late Triassic (Late Carnian to Early Norian) of North America (SW USA). One rauisuchian, Teratosaurus, was for a long time even considered an early theropod dinosaur see for example Colbert, E.H., 1961, Dinosaurs: Their Discovery and Their World, Dutton, New York, 1961 p.67, but was later shown to be nondinosaurian Galton, P. M. (1985). "The poposaurid thecodontian Teratosaurus suevicus von Meyer, plus referred specimens mostly based on prosauropod dinosaurs". Stuttgarter Beitrage zur Naturkunde, B, 116: 1-29.Benton, M.J. (1986). "The late Triassic reptile Teratosaurus - a rauisuchian, not a dinosaur". Palaeontology 29: 293-301.. References Further Reading * Carroll, R. L. (1988). Vertebrate Paleontology and Evolution. New York: WH Freeman & Co. ISBN 0716718227. External links * Translation and Pronunciation Guide *Palaeos Category:Rauisuchians